Gelatine : a protein

II) Gelatine is actually a protein

  As we showed in a previous part of our report, gelatin is produced by partial hydrolysis of collagen.
It's a « small protein » or a polypeptide which has structuring properties just like its parent collagen.
According to our researches, gelatin counts 18 different amino-acids with various concentration. Its carecteristic is a high level of prolin, hydroxyproline as well as glycine.
These amino-acids are connected with each other so that they form polypeptide chains of which contains more than a thousand amino-acids.
Gelatine structure is a stick-shaped molecule (a protofibrille) composed of primary, secondary and tertiary helicoïd structures.

the structural unit of the gelatin

  As we know, gelatine leaves are made of 90% of protein, 2% of salt and the rest of water. Quickly, we achieved that it had to be the protein which made the gelatine keep its shape.

  We knew that it was infeasible to cook a Jelly pineapple. Indeed, it's common knowledge that it doesn't gelify.
Armed with this assertion, we wondered why. It's after a few research that we found out an interesting thing about pineapple. It contains an enzyme, bromelin which among others had the property to make the milk curdle but also to denaturate protein in a irreversible way.

Experiment 1 : the pineapple jelly.

  Hypothesis: The protein structure allows the gelatine set.

  Material : 2 gelatine leaves
                  A cup of water
                  A raw pineapple
                  A bowl

1) Cook a « water-Jelly » :Put the gelatin leaves into the water for 10 min to make it swell
                                                     Drain it
                                                   Add the swelled jelly into the heated water
                                                    Stir it until its dissolution
                                                    Put it in the frigde for 16 hours
2) Slip some raw-pineapple pieces into the set jelly.
3) Wait a couple of hours.

  Observation: We can see that the set jelly is now liquid. Some pineapple pieces are drifting on it.

  Interpretation : The bromelin has denatured the gelatine protein.

Related experience :

  To check whether the pineapple's enzymes sparked really off the liquid Jelly, we realised the same experience with heated pineapple which contained a denature version of the bromelin (As we know, heating an enzyme causes its denaturation) instead of raw pineapple.
After putting the pineapple's pieces into the gelatine, it didn't turn liquid like the previous time.
It assures that our hypothesis is right : the enzymes included in the raw pineapple causes the liquefaction of the jelly. It also shows that the protein included into the gelatine is important for the set of the jelly.

  It has to be said that a similar effect is obtained with kiwi or papaya because they also include some enzymes which are able to do such a proteolysis.




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